Simultaneous detection of ambient methane, nitrous oxide, and water vapor using an external-cavity quantum cascade laser

A compact laser-based absorption sensor system associated with a 152-m path length absorption cell for simultaneous second harmonic (2f) detection of atmospheric nitrous oxide (N2O), methane (CH4), and water vapor (H2O) is presented. An 8 mu m external cavity quantum cascade laser (EC-QCL) was used as an excitation source to simultaneously target three neighboring absorption lines, N2O at 1255.424 cm(-1) , CH4 at 1255.000 cm(-1), and H2O at 1254.732 cm(-1) . Minimum detection limits (1 sigma) of 0.9 ppb for N2O, 4.8 ppb for CH4 and 31 ppm for H2O were achieved with a 1.s integration time at an optimum pressure of 50 Torr. Both laboratory and atmospheric environmental mixing ratios of these three gases associated with basic meteorological parameters were recorded and the corresponding emission sources were analyzed. In particular, the N2O emission was studied during extended time periods including rainy intervals.